Processing method of wafer

ABSTRACT

A processing method of a wafer includes a resist film coating step of coating either one surface of a front surface and a back surface with a resist film containing an ultraviolet absorber, a laser beam irradiation step of irradiating the side of the one surface with a laser beam absorbed by the wafer and removing part of the wafer and the resist film along planned dividing lines, a plasma etching step of supplying a gas in a plasma state to the side of the one surface and removing an exposed region of the wafer exposed along the planned dividing lines through plasma etching, and a check step of irradiating plural positions on the side of the one surface of the wafer with ultraviolet rays and detecting light emission of the resist film to measure the thickness of the resist film and check a coating state of the resist film.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a processing method of a wafer in whichplasma etching is executed for the wafer on which devices are formed onthe front surface side and the wafer is processed.

Description of the Related Art

It is known that a wafer is split by a cutting blade or laser beam whenthe wafer on which a device is formed in each of regions marked out byplural planned dividing lines set in a lattice manner on the frontsurface side is divided along the respective planned dividing lines tomanufacture device chips. However, in the case of splitting the wafer bythe cutting blade or laser beam, the planned dividing lines need to besequentially processed one by one. Therefore, there is a problem thatthe processing time of the wafer becomes long with the wafer in whichthe number of planned dividing lines is comparatively large.

Thus, as an efficient splitting method of a wafer, plasma dicing hasbeen devised in which all planned dividing lines are simultaneouslyprocessed by executing plasma etching for the wafer for which the regionother than the planned dividing lines is covered by a resist film.However, the cost becomes very high when patterning of the resist filmis executed by using an expensive stepper and so forth. Thus, as amethod for patterning the resist film more inexpensively, a method hasbeen devised in which a water-soluble resin film containing anultraviolet absorber is used as the resist film and patterning of thisresist film is executed by a laser beam.

Specifically, first, the whole of the front surface of a wafer is coatedwith the water-soluble resin film (i.e. resist film) containing theultraviolet absorber. Next, by executing irradiation with a laser beamhaving a wavelength in the ultraviolet region along planned dividinglines, part of the resist film and part of the front surface side of thewafer are removed by ablation processing along the planned dividinglines. Thereby, the patterning of the resist film is executed (forexample, refer to Japanese Patent Laid-open No. 2016-207737).

SUMMARY OF THE INVENTION

However, the above-described resist film is almost transparent tovisible light and therefore it is difficult to visually distinguishwhether or not the resist film is formed on the wafer. If plasma etchingis executed for the wafer in the state in which the resist film is notformed partly or is not formed at all, processing failures such asdamage on a device and unevenness of the thickness of the device chipoccur. The present invention is made in view of this problem and intendsto detect processing failure or suppress the occurrence of processingfailure in the case of executing plasma etching for a wafer with use ofa resist film.

In accordance with an aspect of the present invention, there is provideda processing method of a wafer on which a device is formed in each of aplurality of regions marked out by a plurality of planned dividing linesset to intersect each other on the side of a front surface. Theprocessing method includes a resist film coating step of coating eitherone surface of the front surface and a back surface located on theopposite side to the front surface with a resist film containing anultraviolet absorber and a laser beam irradiation step of irradiatingthe side of the one surface coated with the resist film with a laserbeam having such a wavelength as to be absorbed by the wafer andremoving part of the wafer and the resist film along the planneddividing lines. The processing method includes also a plasma etchingstep of supplying a gas in a plasma state to the side of the one surfaceand removing an exposed region of the wafer exposed along the planneddividing lines through plasma etching after the laser beam irradiationstep and a check step of irradiating a plurality of positions on theside of the one surface of the wafer with ultraviolet rays and detectinglight emission of the resist film that absorbs the ultraviolet rays tomeasure the thickness of the resist film at each of the positions andcheck a coating state of the resist film after the resist film coatingstep.

Preferably, the check step includes a post-etching check step executedafter the plasma etching step, and whether or not a film thicknessinsufficiency region in which the thickness of the resist film issmaller than a first threshold exists is detected in the post-etchingcheck step.

Furthermore, preferably, the check step includes a pre-etching checkstep executed after the resist film coating step and before the laserbeam irradiation step and the plasma etching step, and the resist filmcoating step is executed again if a film thickness insufficiency regionin which the thickness of the resist film is smaller than a secondthreshold is detected in the pre-etching check step.

Moreover, preferably, the one surface is the front surface on which thedevice is formed, and the side of the front surface is coated with theresist film in the resist film coating step.

The processing method of a wafer according to the aspect of the presentinvention includes the resist film coating step of coating the onesurface of the wafer with the resist film containing the ultravioletabsorber and the check step of detecting light emission of the resistfilm to measure the thickness of the resist film at each of pluralpositions on the wafer and check the coating state of the resist filmafter the resist film coating step. Whether the resist film properlycoats the wafer can be checked by the check step. For example, in thecase of executing the check step after the plasma etching step, it canbe checked whether the plasma etching has been executed for the wafer inthe state in which the resist film is not formed partly or is not formedat all. Therefore, the device estimated to be damaged and a device chipestimated to have become uneven in the thickness can be detected.Moreover, in the case of executing the check step after the resist filmcoating step and before the laser beam irradiation step and the plasmaetching step, it is possible to prevent the situation in which theplasma etching is executed for the wafer in the state in which theresist film is not formed partly or is not formed at all. Therefore,processing failures such as damage on the device and unevenness of thethickness of the device chip can be suppressed.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing some preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a wafer and so forth;

FIG. 2 is a perspective view of a laser processing apparatus;

FIG. 3 is a diagram illustrating how a water-soluble resin is appliedonto one surface of the wafer;

FIG. 4 is an outline diagram of a film thickness measuring instrument;

FIG. 5 is a graph illustrating the outline of the relationship betweenthe thickness of a resist film and the emission intensity;

FIG. 6A is a sectional view illustrating one example of the wafer aftera resist film coating step;

FIG. 6B is a sectional view illustrating another example of the waferafter the resist film coating step;

FIG. 7A is a diagram illustrating a laser beam irradiation step;

FIG. 7B is a sectional view of the wafer after the laser beamirradiation step;

FIG. 8A is a diagram illustrating a remote plasma etching step;

FIG. 8B is a sectional view of the wafer and so forth split by a directplasma etching step;

FIG. 9 is a diagram illustrating a post-etching check step;

FIG. 10 is a flowchart of a processing method of a wafer according to afirst embodiment; and

FIG. 11 is a flowchart of a processing method of a wafer according to asecond embodiment.

DETAILED DESCRIPTON OF THE PREFERRED EMBODIMENTS

Embodiments according to an aspect of the present invention will bedescribed with reference to the accompanying drawings. First, a wafer 11processed in a first embodiment will be described. FIG. 1 is aperspective view of the wafer 11 and so forth. The wafer 11 has acircular disc shape and includes a front surface 11 a having asubstantially circular shape and a back surface 11 b that has asubstantially circular shape and is located on the opposite side to thefront surface 11 a. Plural planned dividing lines 13 are set in such amanner as to intersect each other on the side of the front surface 11 aof the wafer 11.

A device 15 such as an integrated circuit (IC), a large scaleintegration (LSI) circuit, or a light emitting diode (LED) is formed ineach of plural regions marked out by the plural planned dividing lines13. The wafer 11 of the present embodiment has a circular-disc-shapedsubstrate 11 c formed of silicon and a functional layer 15 a (see FIG.6A and FIG. 6B) that is disposed on the substrate 11 c and is located onthe side of the front surface 11 a. The functional layer 15 a is amultilayer interconnect layer in which interlayer insulating filmsformed of a low dielectric constant material (what is called Low-kmaterial) and metal interconnect layers are alternately stacked.

Regions corresponding to the planned dividing lines 13 in the functionallayer 15 a are lower than regions corresponding to the devices 15 andtest element groups (TEG) 15 b (see FIG. 6A and FIG. 6B) formed of ametal are discretely formed in these regions along the planned dividinglines 13. Although the substrate 11 c in the present embodiment iscomposed of a semiconductor material such as silicon, there is no limiton the material, shape, structure, size, and so forth of the substrate11 c. Similarly, there is no limit also on the kind, quantity, shape,structure, size, arrangement, and so forth of the devices 15.

When the wafer 11 is processed, a wafer unit 21 composed of the wafer11, a dicing tape 17, and an annular frame 19 is formed as illustratedin FIG. 1. The dicing tape 17 is a circular tape having a diameterlarger than the diameter of the wafer 11. The dicing tape 17 has astacking structure of a base layer and an adhesion layer (glue layer),for example. The base layer is formed of a resin such as polyolefin (PO)and the adhesion layer formed of a resin with adhesiveness, such as anultraviolet (UV)-curable resin, is formed on the whole or part of onesurface of the base layer.

The wafer 11 is stuck to a substantially central part of the base layerwith the intermediary of the adhesion layer and one surface of theannular frame 19 formed of a metal is stuck to the peripheral part ofthe base layer with the intermediary of the adhesion layer. Thereby, thewafer unit 21 in which the wafer 11 is supported by the frame 19 withthe intermediary of the dicing tape 17 is formed. The dicing tape 17 isnot limited to the stacking structure of the base layer and the adhesionlayer. For example, the dicing tape 17 may have only the base layer. Inthis case, by executing thermal compression bonding of the base layer tothe wafer 11 and so forth, the dicing tape 17 is stuck to the wafer 11and so forth and the wafer unit 21 is formed.

The wafer 11 is conveyed to a laser processing apparatus to be processedin the form of the wafer unit 21. FIG. 2 is a perspective view of alaser processing apparatus 2. In FIG. 2, part of constituent elements ofthe laser processing apparatus 2 is illustrated by a functional block.Furthermore, in the following description, an X-axis direction(processing feed direction), a Y-axis direction (indexing feeddirection), and a Z-axis direction (vertical direction, heightdirection) are perpendicular to each other. The laser processingapparatus 2 includes a base 4 that supports each structure. A protrudingpart 4 a is disposed in such a manner as to protrude in the Z-axisdirection at a corner part of the base 4. A space is formed inside theprotruding part 4 a and a cassette elevator 8 that can rise and loweralong the Z-axis direction is disposed in this space. A cassette 10 inwhich plural wafer units 21 are housed is placed on the upper surface ofthe cassette elevator 8.

A temporary placement mechanism 12 for temporarily placing the wafer 11is disposed on one side of the protruding part 4 a in the Y-axisdirection. The temporary placement mechanism 12 includes a pair of guiderails 12 a and 12 b that get closer to or further away from each otherwhile keeping the state of being parallel to the Y-axis direction. Thetemporary placement mechanism 12 adjusts the position of the wafer unit21 in the X-axis direction to a predetermined position by sandwichingthe wafer unit 21 in the X-axis direction. A conveying mechanism 14 thatconveys the wafer unit 21 is disposed above the temporary placementmechanism 12.

The conveying mechanism 14 has a gripping part 14 a for gripping part ofthe frame 19. The conveying mechanism 14 draws out the wafer unit 21from the cassette 10 to the temporary placement mechanism 12 in thestate in which the frame 19 is gripped by the gripping part 14 a. Asuction mechanism (not illustrated) that sucks and holds plural placeson the frame 19 is disposed at the bottom part of the conveyingmechanism 14. The wafer unit 21 sucked and held by the suction mechanismis conveyed to an applying-cleaning unit 16 and a chuck table 38 thatwill be described later by the conveying mechanism 14.

The applying-cleaning unit 16 is disposed on one side of the temporaryplacement mechanism 12 in the Y-axis direction. The applying-cleaningunit 16 has a circular cylindrical space and a spinner table 16 a thatcan rotate in the state of sucking and holding the wafer unit 21 isdisposed in this circular cylindrical space. A rotational drive source(not illustrated) such as a motor that rotates the spinner table 16 a iscoupled to the lower part of the spinner table 16 a. An applying nozzle16 b that jets a water-soluble resin 23 (see FIG. 3) to which anultraviolet absorber is added is disposed near the spinner table 16 a.As the ultraviolet absorber, a benzophenone-based, benzotriazole-based,triazine-based, or benzoate-based ultraviolet absorber is used, forexample. Furthermore, as the water-soluble resin 23, polyvinyl alcohol(PVA), polyethylene glycol (PEG), or polyethylene oxide (PEO) is used,for example.

A cleaning nozzle 16 c (see FIG. 2) is disposed at a different positionfrom the applying nozzle 16 b near the spinner table 16 a. The cleaningnozzle 16 c jets binary fluid obtained by mixing water and air, forexample. A horizontal movement mechanism 20 is disposed on the frontsurface (upper surface) of the base 4 located on one side in the X-axisdirection with respect to the applying-cleaning unit 16. The horizontalmovement mechanism 20 includes a pair of Y-axis guide rails 22 that arefixed to the upper surface of the base 4 and are parallel to the Y-axisdirection. A Y-axis moving table 24 is slidably attached to the Y-axisguide rails 22.

A nut part (not illustrated) is disposed on the back surface side (lowersurface side) of the Y-axis moving table 24, and a Y-axis ball screw 26parallel to the Y-axis guide rails 22 is joined to this nut part in sucha manner as to be rotatable. A Y-axis pulse motor 28 is coupled to oneend part of the Y-axis ball screw 26. When the Y-axis ball screw 26 isrotated by the Y-axis pulse motor 28, the Y-axis moving table 24 movesin the Y-axis direction along the Y-axis guide rails 22. A pair ofX-axis guide rails 30 parallel to the X-axis direction are disposed onthe front surface (upper surface) of the Y-axis moving table 24.

An X-axis moving table 32 is slidably attached to the X-axis guide rails30. A nut part (not illustrated) is disposed on the back surface side(lower surface side) of the X-axis moving table 32, and an X-axis ballscrew 34 parallel to the X-axis guide rails 30 is joined to this nutpart in such a manner as to be rotatable. An X-axis pulse motor (notillustrated) is coupled to one end part of the X-axis ball screw 34.When the X-axis ball screw 34 is rotated by the X-axis pulse motor, theX-axis moving table 32 moves in the X-axis direction along the X-axisguide rails 30.

A table base 36 is disposed on the front surface side (upper surfaceside) of the X-axis moving table 32. The chuck table 38 for sucking andholding the wafer 11 is disposed at the upper part of the table base 36.Four clamps 40 that fix the frame 19 from four sides are disposed aroundthe chuck table 38. The bottom part of the chuck table 38 is coupled toa rotational drive source (not illustrated) such as a motor disposedinside the table base 36, and the chuck table 38 can rotate around therotation axis parallel to the Z-axis direction. The upper surface of thechuck table 38 functions as a holding surface 38 a that sucks and holdsthe wafer unit 21.

The holding surface 38 a is connected to a suction source (notillustrated) such as an ejector through a suction path (not illustrated)and so forth formed inside the chuck table 38 and the table base 36.When the suction source is operated, a negative pressure is generatedfor the holding surface 38 a. At an end part of the base 4 on one sidein the Y-axis direction, a wall-shaped support structure 6 that extendsalong the Z-axis direction is disposed. A support arm 6 a that protrudestoward the center side of the base 4 is disposed on the supportstructure 6. A light collector 42 that emits a laser beam downward isdisposed at the tip part of this support arm 6 a.

A laser osci11ator (not illustrated) for generating a pulsed laser beamis optically connected to the light collector 42. The light collector42, the laser osci11ator, and so forth configure a laser beamirradiation unit. The laser beam emitted from the light collector 42 hassuch a wavelength as to be absorbed by the wafer 11. The wavelength ofthis laser beam is a wavelength in the ultraviolet region (for example,355 nm). Furthermore, the average output power of this laser beam isadjusted to 0.5 W, for example, and the repetition frequency of thepulse of this laser beam is adjusted to 200 kHz, for example.

A measuring head 44 a of a film thickness measuring instrument 44 isdisposed on one side of the light collector 42 in the X-axis direction.Here, the film thickness measuring instrument 44 will be described withreference to FIG. 4. FIG. 4 is an outline diagram of the film thicknessmeasuring instrument 44. In FIG. 4, part of constituent elements of thefilm thickness measuring instrument 44 is illustrated by functionalblocks. The film thickness measuring instrument 44 has a light source 44b for measurement. The light source 44 b for measurement is anultraviolet (UV) light that executes irradiation with ultraviolet rays,for example. However, the light source 44 b for measurement may be alaser osci11ator that executes irradiation with a laser beam havinglower output power than the laser beam emitted from the light collector42 and a wavelength in the ultraviolet region. Part of the ultravioletrays emitted from the light source 44 b for measurement is transmittedthrough a half mirror 44 c and is reflected by a mirror 44 d to beincident on a collecting lens 44 e disposed in the measuring head 44 a.The wafer unit 21 held by the holding surface 38 a is disposed below themeasuring head 44 a.

The wafer unit 21 illustrated in FIG. 4 is held by the holding surface38 a in such a manner that the front surface (one surface) 11 a of thewafer 11 is exposed. A resist film 25 containing the ultravioletabsorber is formed on the front surface 11 a of the wafer 11. Theultraviolet rays emitted from the collecting lens 44 e are incident onthe resist film 25 on the side of the front surface 11 a in such amanner as to be collected on the side of the front surface 11 a of thewafer 11. The ultraviolet absorber in the resist film 25 absorbs theultraviolet rays and emits light. For example, the ultraviolet absorberabsorbs the ultraviolet rays and emits fluorescence in a predeterminedband (for example, from 360 nm to 560 nm inclusive).

The fluorescence goes through the collecting lens 44 e, the mirror 44 d,and the half mirror 44 c sequentially and is incident on a lightreceiving part 44 f. The light receiving part 44 f has an imagingelement (not illustrated) such as a complementary metal oxidesemiconductor (CMOS) image sensor or charge coupled device (CCD) imagesensor, for example. The fluorescence incident on the light receivingpart 44 f is subjected to photoelectric conversion by the imagingelement and is converted to a voltage signal corresponding to theemission intensity. This voltage signal is sent to a control part 48(see FIG. 2) to be described later and the thickness of the resist film25 according to the voltage signal is calculated.

The ultraviolet absorber is evenly dispersed in the resist film 25.Therefore, when the resist film 25 is irradiated with ultraviolet rayswith predetermined output power, the emission intensity of thefluorescence becomes higher when the resist film 25 is thicker. FIG. 5is a graph illustrating the outline of the relationship between thethickness of the resist film 25 and the emission intensity. The abscissaaxis of FIG. 5 indicates the thickness (nm) of the resist film 25 andthe ordinate axis of FIG. 5 indicates the intensity (a.u.) of thefluorescence incident on the light receiving part 44 f. When the resistfilm 25 is absent (that is, the thickness is zero), the intensity of thefluorescence is zero. As the thickness of the resist film 25 increases,the intensity of the fluorescence increases. The thickness of the resistfilm 25 is measured at plural positions on the side of the front surface11 a. In this case, for example, the horizontal movement mechanism 20 isoperated and the front surface 11 a is scanned with ultraviolet raysemitted from the light source 44 b for measurement. As the measurementmethod of the thickness of the resist film 25, the thickness of theresist film 25 may be measured based on the correspondence relationshipbetween the emission intensity of the fluorescence and a predeterminedwavelength band as disclosed in Japanese Patent Laid-open No.2012-104532.

Here, referring back to FIG. 2, other constituent elements of the laserprocessing apparatus 2 will be described. An imaging head 46 of a cameraunit for imaging the wafer 11 is disposed on the opposite side to themeasuring head 44 a across the light collector 42. This camera unit is avisible light camera unit (not illustrated) or infrared (IR) camera unit(not illustrated) and is used for alignment and kerf check of the wafer11, for example. Furthermore, the laser processing apparatus 2 has thecontrol part 48 connected to the respective constituent elements such asthe conveying mechanism 14, the applying-cleaning unit 16, thehorizontal movement mechanism 20, the chuck table 38, the laser beamirradiation unit, the film thickness measuring instrument 44, and thecamera unit. The control part 48 controls the respective constituentelements according to the series of steps necessary for processing ofthe wafer 11.

The control part 48 is configured by a computer including a processingapparatus such as a central processing unit (CPU) and a storingapparatus such as a flash memory. By causing the processing apparatus tooperate in accordance with software such as a program stored in thestoring apparatus, the control part 48 functions as specific means inwhich the software and the processing apparatus (hardware resources)cooperate. The control part 48 has a calculating section (notillustrated) that calculates the thickness of the resist film 25according to the voltage signal from the light receiving part 44 f. Thiscalculating section is a program stored in the storing apparatus, forexample. The calculating section reads out the correspondencerelationship between the intensity of fluorescence and the thickness ofthe resist film 25 stored in a partial region of the storing apparatusand calculates the thickness of the resist film 25 based on thiscorrespondence relationship. The correspondence relationship between theintensity of fluorescence and the thickness of the resist film 25 readout from the storing apparatus by the calculating section is anexpression to identify the graph illustrated in FIG. 5, a table obtainedin advance, or the like, for example.

Next, processing methods of the wafer 11 will be described. FIG. 10 is aflowchart of the processing method of the wafer 11 according to thefirst embodiment. In the present embodiment, first, the front surface 11a of the wafer 11 is coated with the resist film 25 by using theapplying-cleaning unit 16 (resist film coating step (S10)). In theresist film coating step (S10), first, the wafer unit 21 is conveyed tothe applying-cleaning unit 16, and the wafer unit 21 is sucked and heldby the spinner table 16 a in such a manner that the front surface (onesurface) 11 a is exposed.

Next, in the state in which the spinner table 16 a is rotated, thewater-soluble resin 23 in a liquid state containing the ultravioletabsorber is jetted from the applying nozzle 16 b. FIG. 3 is a diagramillustrating how the water-soluble resin 23 is applied onto one surfaceof the wafer 11. The water-soluble resin 23 spreads outward due to acentrifugal force and the water-soluble resin 23 is applied on the wholeof the front surface 11 a of the wafer 11. After the application, thewater-soluble resin 23 is dried and thereby the water-soluble resin 23becomes the resist film 25. That is, the whole of the front surface 11 ais coated with the resist film 25 containing the ultraviolet absorber.

FIG. 6A is a sectional view illustrating one example of the wafer 11after the resist film coating step (S10). The resist film 25 illustratedin FIG. 6A is formed with an even thickness in the region correspondingto the devices 15 and the planned dividing lines 13. However, a hole 25a or an application unevenness (a region in which the thickness is largeor small partly) is formed in the resist film 25 in some cases due tofactors such as the viscosity of the water-soluble resin 23, thewettability of the front surface 11 a, and the number of rotations ofthe spinner table 16 a per unit time.

FIG. 6B is a sectional view illustrating another example of the wafer 11after the resist film coating step (S10). In the resist film 25illustrated in FIG. 6B, the hole 25 a is formed over the device 15. Ifthe hole 25 a exists, this becomes a cause of the occurrence ofprocessing failures such as damage on the device 15 and unevenness ofthe thickness of the device chip in a plasma etching step to bedescribed later. In the present embodiment, after the resist filmcoating step (S10), the side of the front surface 11 a is irradiatedwith a laser beam by using the laser beam irradiation unit with thelight collector 42 and so forth, and the resist film 25 and part of thewafer 11 are removed along the planned dividing lines 13 (laser beamirradiation step (S20)).

FIG. 7A is a diagram illustrating the laser beam irradiation step (S20).In the laser beam irradiation step (S20), first, the wafer unit 21 isconveyed to the chuck table 38. Then, by using the visible light cameraunit, alignment of the wafer 11 is executed and one planned dividingline 13 is positioned parallel to the X-axis direction. Next, in thestate in which irradiation with the laser beam from the light collector42 is executed, the light collector 42 and the chuck table 38 arerelatively moved along the X-axis direction. Thereby, the resist film 25and part of the wafer 11 are subjected to ablation processing and areremoved along the one planned dividing line 13.

After the irradiation with the laser beam is executed along the oneplanned dividing line 13, indexing feed of the chuck table 38 isexecuted. Then, irradiation with the laser beam is similarly executedalong another planned dividing line 13 adjacent to the planned dividingline 13 after the processing in the Y-axis direction. After irradiationwith the laser beam is executed along all planned dividing lines 13parallel to the X-axis direction, the chuck table 38 is rotated by 90degrees. Then, irradiation with the laser beam is similarly executedalong the remaining planned dividing lines 13 for which processing hasnot been executed. Thereby, the resist film 25 and part of the wafer 11are subjected to ablation processing along all planned dividing lines 13and grooves 11 d that are exposed regions of the wafer 11 are formed onthe side of the front surface 11 a.

FIG. 7B is a sectional view of the wafer 11 after the laser beamirradiation step (S20). Debris 25 b generated in association with theablation processing often adheres to the resist film 25 after the laserbeam irradiation step (S20), and a heat affected layer (not illustrated)arising from alteration due to heat is often formed in the groove 11 d.After the laser beam irradiation step (S20), a plasma etching apparatus(not illustrated) set separately from the laser processing apparatus 2is used to supply a gas in a plasma state to the side of the frontsurface 11 a and execute etching of the wafer 11 (plasma etching step(S30)).

The plasma etching apparatus has a chamber (not illustrated) formed of ametal. In the chamber, a door part (not illustrated) that serves as aconveyance path of the wafer unit 21 is disposed. Furthermore, anevacuation apparatus (not illustrated) for evacuating the inside isconnected to the chamber. A table base (not illustrated) is disposed inthe chamber. In the table base, an electrostatic chuck (not illustrated)that holds the wafer unit 21 and a bias electrode (not illustrated) thatis electrically isolated from the electrostatic chuck and is connectedto a high-frequency power supply (not illustrated) through a blockingcapacitor (not illustrated) are disposed.

An applicator (not illustrated) for generating remote plasma is disposedon the ceiling part of the chamber located above the table base. Theapplicator includes a gas supply pipe (not illustrated) connected to theceiling part of the chamber substantially perpendicularly, a wave-guidepipe (not illustrated) connected to the gas supply pipe in such a manneras to be substantially orthogonal to the gas supply pipe, and ahigh-frequency generation source (not illustrated) disposed on one endside of the wave-guide pipe. To the gas supply pipe, an inert gas supplysource (not illustrated) having an inert gas of helium (He), argon (Ar),or the like, a first fluorine-based gas supply source having a firstfluorine-based gas (SF₆), and a second fluorine-based gas supply sourcehaving a second fluorine-based gas (C₄F₈) are connected.

In the plasma etching step (S30), first, the wafer unit 21 is conveyedto the electrostatic chuck and the wafer unit 21 is held by theelectrostatic chuck (not illustrated) in such a manner that the frontsurface 11 a is exposed. In the present embodiment, by use of the plasmaetching apparatus, first a remote plasma etching step (S32) is executedfor the wafer 11 and subsequently a direct plasma etching step (S34) isexecuted.

In the remote plasma etching step (S32), the inert gas and the SF₆ gasare supplied to the gas supply pipe and these gases are irradiated witha microwave of 2.45 GHz and 2000 W through the wave-guide pipe. Thegases turned to plasma by the microwave (remote plasma P1) reach thewafer 11 from the applicator and etch the bottom parts and side parts ofthe grooves 11 d. FIG. 8A is a diagram illustrating the remote plasmaetching step (S32). In the remote plasma etching step (S32), the heataffected layer at the bottom parts and the side parts of the grooves 11d and the debris 25 b that adheres to the inside of the grooves 11 d areremoved.

After the remote plasma etching step (S32), the inside of the chamber isevacuated. Furthermore, the bottom parts of the grooves 11 d are etchedand removed by plasma generated in the chamber (direct plasma P2)(direct plasma etching step (S34)). In the direct plasma etching step(S34), the substrate 11 c is split by etching the bottom parts of thegrooves 11 d by what is called the Bosch process. Specifically, the SF₆gas is supplied from the first fluorine-based gas supply source to thechamber for a first predetermined time and high-frequency power of 13.56MHz and 300 W is applied to the bias electrode. The substrate 11 c isisotropically etched by the SF₆ gas turned to plasma.

Subsequently, the supply of the SF₆ gas from the first fluorine-basedgas supply source is stopped and the C₄F₈ gas is supplied from thesecond fluorine-based gas supply source to the chamber. Thehigh-frequency power of 13.56 MHz and 300 W is applied to the biaselectrode. When the C₄F₈ gas is supplied for a second predetermined timein this state, a protective film is formed on the sidewalls of thegrooves 11 d by the C₄F₈ gas turned to plasma. Subsequently, the supplyof the C₄F₈ gas is stopped. Thereafter, in the state in which theabove-described high-frequency power is applied to the bias electrode,the supply of the SF₆ gas for the first predetermined time and thesupply of the C₄F₈ gas for the second predetermined time are alternatelyrepeated. Due to the formation of the protective film on the sidewallsof the grooves 11 d, the bottom parts of the grooves 11 d areselectively etched by the SF₆ gas turned to plasma and finally thesubstrate 11 c is split. FIG. 8B is a sectional view of the wafer 11 andso forth split by the direct plasma etching step (S34).

After the plasma etching step (S30), the coating state of the resistfilm 25 is checked by detecting light emission of the resist film 25 byusing the film thickness measuring instrument 44 (post-etching checkstep (S40)). FIG. 9 is a diagram illustrating the post-etching checkstep (S40). In the post-etching check step (S40), first, the wafer unit21 is taken out from the plasma etching apparatus and is conveyed to thelaser processing apparatus 2, and the wafer unit 21 is held by the chucktable 38 in such a manner that the front surface 11 a is orientedupward.

Subsequently, in the state in which the side of the front surface 11 ais irradiated with ultraviolet rays from the light source 44 b formeasurement, the chuck table 38 is moved by the horizontal movementmechanism 20. Thereby, the resist film 25 is scanned. For example, theirradiation with the ultraviolet rays is executed in such a manner thatthe ultraviolet rays traverse the respective devices 15. Then, thecontrol part 48 checks the thickness of the resist film 25 based onfluorescence from the resist film 25. Because spin coating is executedin the resist coating step (S10), the thickness of the resist film 25tends to be smaller at the peripheral part of the wafer 11. Therefore,in the post-etching check step (S40), the time used for checking theperipheral part of the wafer 11 may be set longer than the time used forchecking the central part of the wafer 11. Specifically, regarding theplural devices 15 located on the peripheral side of the wafer 11 (forexample, 6 pieces×4 of the devices 15 located on the respectiveperipheral sides of X direction and Y direction in FIG. 9), the devices15 are scanned with the ultraviolet rays plural times in such a mannerthat the irradiation position reciprocates on the devices 15.

The thickness of the resist film 25 is at least 2 pm and at most 6 μm,for example, before the plasma etching step (S30). However, after theplasma etching step (S30), the thickness decreases due to the etching.Thus, in the present embodiment, 0.1 μm is set as a first threshold andthe control part 48 detects whether or not a film thicknessinsufficiency region 27 in which the thickness of the resist film 25 issmaller than this first threshold exists in the region excluding theplanned dividing lines 13 on the side of the front surface 11 a.

For example, the film thickness insufficiency region 27 is classifiedinto an attention region in which the thickness of the resist film 25 islarger than 0 μm and is equal to or smaller than the first threshold anda processing failure region in which the thickness of the resist film 25is 0 μm. In the attention region and the surrounding thereof, there is apossibility that a region in which the thickness of the resist film 25is 0 μm exists. Furthermore, in the processing failure region, there isa possibility that the device 15 is damaged. The control part 48 causesa monitor (not illustrated) to display a warning indicating that thewafer 11 in which the processing failure region has been detected is adefective wafer. Instead of issuing the warning indicating that thewafer 11 is a defective wafer, the control part 48 may issue a warningindicating that the device 15 located in a region in which theprocessing failure region has been detected is defective. Furthermore,the control part 48 may cause a monitor of the laser processingapparatus 2 to display the distribution of the attention region and theprocessing failure region.

In the present embodiment, it can be checked whether the plasma etchinghas been executed for the wafer 11 in the state in which the resist film25 is not formed partly or is not formed at all. Therefore, the device15 estimated to be damaged and the device chip estimated to have becomeuneven in the thickness can be detected. After the post-etching checkstep (S40), the resist film 25 is removed (resist film removal step(S50)). In the resist film removal step (S50), first, the wafer unit 21is conveyed from the chuck table 38 to the spinner table 16 a. Then, thewafer unit 21 is held in such a manner that the side of the frontsurface 11 a is oriented upward, and the spinner table 16 a is rotatedand binary fluid is jetted from the cleaning nozzle 16 c. Thereby, theresist film 25 formed of the water-soluble resin 23 dissolves to beremoved. After the wafer 11 is cleaned, the wafer unit 21 is conveyed tothe cassette 10.

Next, a processing method of the wafer 11 according to a secondembodiment will be described. The processing method in the secondembodiment further includes a pre-etching check step (S12) executedafter the resist film coating step (S10) and before the laser beamirradiation step (S20) and the plasma etching step (S30) in addition tothe post-etching check step (S40). FIG. 11 is a flowchart of theprocessing method of the wafer 11 according to the second embodiment.Also in the pre-etching check step (S12), the thickness of the resistfilm 25 is checked at plural positions on the wafer 11 by using the filmthickness measuring instrument 44 similarly to the post-etching checkstep (S40).

In the pre-etching check step (S12), it is checked whether or not thefilm thickness insufficiency region 27 in which the thickness of theresist film 25 is smaller than a second threshold (for example, 2 μm)exists. In consideration of decrease in the thickness of the resist film25 due to the plasma etching, the second threshold is set larger thanthe first threshold. If the film thickness insufficiency region 27 inwhich the thickness of the resist film 25 is smaller than the secondthreshold is detected in the pre-etching check step (S12) (YES in S14),the resist film coating step (S10) is executed again. In this case, theresist film 25 may be further formed on the existing resist film 25, orthe resist film 25 may be formed again on the side of the front surface11 a after the existing resist film 25 is removed by theapplying-cleaning unit 16.

In the pre-etching check step (S12), it is possible to prevent thesituation in which the plasma etching step (S30) is executed for thewafer 11 in the state in which the resist film 25 is not formed partlyor is not formed at all. Therefore, processing failures such as damageon the device 15 and unevenness of the thickness of the device chip canbe suppressed. If the film thickness insufficiency region 27 in whichthe thickness of the resist film 25 is smaller than the second thresholdis not detected by the control part 48 in the pre-etching check step(S12) (NO in S14), the processing method proceeds to the laser beamirradiation step (S20). The subsequent process is the same as the firstembodiment.

Next, a third embodiment will be described. In the third embodiment, inthe resist film coating step (S10), the resist film 25 is formed on theback surface (one surface) 11 b instead of the front surface 11 a. Inthis case, an infrared camera unit is used when alignment of the wafer11 is executed in the laser beam irradiation step (S20). Furthermore,the plasma etching step (S30) and so forth executed for the side of thefront surface 11 a in the first and second embodiments are executed forthe side of the back surface 11 b. Besides, structures, methods, and soforth according to the above-described embodiments can be implementedwith appropriate changes without departing from the range of the objectof the present invention. For example, in the plasma etching step (S30),only the remote plasma etching step (S32) may be executed. In this case,after the resist film removal step (S50), the substrate 11 c is dividedby what is called stealth dicing, for example.

In the stealth dicing, irradiation with a laser beam having such awavelength as to transmit through the wafer 11 is executed along theplanned dividing lines 13 and thereby a modified layer that is fragilecompared with the region that is not irradiated with the laser beam isformed. Thereafter, an external force or the like is given to split thewafer 11. Furthermore, the wafer 11 may be split by cutting the wafer 11along the planned dividing lines 13 by using a cutting blade after theresist film removal step (S50) instead of the stealth dicing.Incidentally, the post-etching check step (S40) may be executed by notthe above-described laser processing apparatus 2 but a measuringapparatus (not illustrated) having the horizontal movement mechanism 20,the table base 36, the chuck table 38, the film thickness measuringinstrument 44, and so forth.

Moreover, a processing apparatus that is a processing apparatus (notillustrated) set separately from the laser processing apparatus 2 andhas the applying-cleaning unit 16 in addition to the horizontal movementmechanism 20, the table base 36, the chuck table 38, the film thicknessmeasuring instrument 44, and so forth may be used. For example, by usingthis processing apparatus, the resist film coating step (S10), thepre-etching check step (S12), the post-etching check step (S40), and theresist film removal step (S50) can be executed. Therefore, by using theprocessing apparatus and the laser processing apparatus 2 incombination, simultaneously with execution of the laser beam irradiationstep (S20) for one wafer 11 by the laser processing apparatus 2, thepost-etching check step (S40) and so forth can be execute for anotherwafer 11 by the processing apparatus. Accordingly, in this case, devicechips can be efficiently manufactured.

The present invention is not limited to the details of the abovedescribed preferred embodiments. The scope of the invention is definedby the appended claims and all changes and modifications as fall withinthe equivalence of the scope of the claims are therefore to be embracedby the invention.

What is claimed is:
 1. A processing method of a wafer on which a deviceis formed in each of a plurality of regions marked out by a plurality ofplanned dividing lines set to intersect each other on a side of a frontsurface, the processing method comprising: a resist film coating step ofcoating either one surface of the front surface and a back surfacelocated on an opposite side to the front surface with a resist filmcontaining an ultraviolet absorber; a laser beam irradiation step ofirradiating a side of the one surface coated with the resist film with alaser beam having such a wavelength as to be absorbed by the wafer andremoving part of the wafer and the resist film along the planneddividing lines; a plasma etching step of supplying a gas in a plasmastate to the side of the one surface and removing an exposed region ofthe wafer exposed along the planned dividing lines through plasmaetching after the laser beam irradiation step; and a check step ofirradiating a plurality of positions on the side of the one surface ofthe wafer with ultraviolet rays and detecting light emission of theresist film that absorbs the ultraviolet rays to measure thickness ofthe resist film at each of the positions and check a coating state ofthe resist film after the resist film coating step.
 2. The processingmethod of a wafer according to claim 1, wherein the check step includesa post-etching check step executed after the plasma etching step, andwhether or not a film thickness insufficiency region in which thethickness of the resist film is smaller than a first threshold exists isdetected in the post-etching check step.
 3. The processing method of awafer according to claim 1, wherein the check step includes apre-etching check step executed after the resist film coating step andbefore the laser beam irradiation step and the plasma etching step, andthe resist film coating step is executed again if a film thicknessinsufficiency region in which the thickness of the resist film issmaller than a second threshold is detected in the pre-etching checkstep.
 4. The processing method of a wafer according to claim 1, whereinthe one surface is the front surface on which the device is formed, andthe side of the front surface is coated with the resist film in theresist film coating step.